It is well known in the art that DC-to-DC converters are utilized to increase and decrease voltage levels within a system. One way to accomplish such conversion is to use a voltage controlled oscillator as a control element within this converter. This VCO feedback circuit typically has been arranged with other feedback loops forming the DC-to-DC converter.
A varying amount of current provided to the base of a bipolar transistor determines the output voltage generated. Problems with this approach exist with regard to the stability of such a circuit. For example, in some situations, the DC-to-DC circuit is required to run at a low frequency, which interferes with the frequency of the VCO causing the VCO to output spurious signals. Additional problems exist in the fact that DC-to-DC converters are part of an operational amplifier driving a loop filter for a VCO resulting in a closed-loop filter and a closed-loop operational amplifier fixed together. Variations of component tolerances with this arrangement produce stability problems.
For instance, a transistor with a large beta or gain variation modifies the bandwidth of the operational amplifier loop, thereby creating instability. Also, as the number of feedback loops increases instability due to component variations becomes more and more problematic. Accordingly, problems with oscillation frequency level and instability make the existing DC-to-DC converters unsuitable for many applications. Furthermore, the complexity of existing DC-to-DC converter circuits requires a user to compute various component values needed for specific bandwidths, input voltages and output voltages, all of which, once selected, are difficult to change for changing situations.
There exists a desire for a low cost DC-to-DC converter which produces few spurious emissions, provides simple computation of required components and input values, operates at easily controllable frequencies and is operable to produce output to input ratio of voltages, in the order of 6 to 1 or more.
The present invention is directed to a system and method which utilizes a fixed base current to control the output voltage instead of a variable base current. In one embodiment, instead of modulating the base current, the converter uses output current to determine the voltage produced at the output. The high output impedance allows a fairly low modulating current to offer a large change in output voltage. This circuit eliminates at least one of the feedback loops found in existing designs, further increasing stability. As a result of the circuit design, there is achieved a DC-to-DC converter which allows the user to easily define the frequency at which the circuit operates and which is tolerant of component variations.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.